This invention relates to the management of logical volumes stacked in data storage media stored in an automated data storage library, and, more particularly, to the expiration of selected logical volumes.
Automated data storage libraries are provided in data processing computer systems for storing vast quantities of data that may be retrieved in reasonable time. The data is typically stored on data storage media, such as magnetic tape in a tape cartridge or cassette, or an optical disk or cartridge. The capacity of such media is considerable, and is much greater than the average size of a data set for most application programs. Consequently, multiple logical volumes of data are xe2x80x9cstackedxe2x80x9d in a single data storage media or xe2x80x9cphysical volumexe2x80x9d. Commonly assigned U.S. Pat. No. 5,546,557 describes the creation and management of such logical volumes and the associated data storage media in an automated data storage library.
A mapping database is conventionally maintained by a library server which identifies each logical volume in the library and maps the logical volumes to the data storage media.
Cache storage is conventionally provided in automated data storage libraries to provide a quick access to data, for example, in a hard disk drive, without waiting for the data storage media to be accessed and loaded into a drive unit to be read and/or written. The data storage media, the storage shelves on which the media are stored, the accessor(s) for accessing the data storage media, and the drive units reading and/or writing data on the data storage media are called xe2x80x9cbacking storagexe2x80x9d.
Often, logical volumes recalled from backing storage data storage media are again accessed, and often updated, within a short period of time. Thus, by having the logical volumes in cache storage, they may be quickly accessed. Conventionally, the logical volumes are variable in length, so that an updated logical volume may be longer or shorter in length than the original. Hence, when an updated logical volume in cache storage is returned to the backing storage data storage media, or xe2x80x9cmigratedxe2x80x9d, it is typically not returned to the same location on the media, and often is written instead to a new or reclaimed data storage media.
A new data storage media, or physical volume, is called a xe2x80x9cSCRATCHxe2x80x9d physical volume, and the logical volumes will be defined as they are written, and identified and mapped to the data storage media by the library server in the mapping database. The original logical volumes that have been updated and rewritten elsewhere are no longer tracked by the library server in the mapping database.
On occasion, the library server will operate a library manager to reclaim a physical volume so that the physical volume becomes a xe2x80x9cSCRATCHxe2x80x9d volume. All of the non-expired logical volumes are read from the backing storage physical volume data storage media into cache storage and are rewritten onto another physical volume without updating, leaving the first physical volume as a xe2x80x9cSCRATCHxe2x80x9d volume which may be entirely rewritten.
Often, a host system will no longer need data. For example, the data is expired because of age or other reasons. The host system may identify the affected logical volumes as expired. However, the library server has no means to reflect this host-originated change in the server""s mapping database. Thus, the library server continues to manage the logical volumes as active data. Since the host considers the data to be expired, the host will not recall and will not update the data. The data is therefore carried indefinitely in the mapping database as though it were active. The continued management of the expired logical volumes requires that each of the volumes must be saved and rewritten during any reclaim procedure. As the result, much of the processing time of the library server and library manager and much of the activity of the backing storage and of the cache storage in reclaiming the physical volumes will be wasted in saving the host-expired logical volumes.
The logical volumes that have been expired by the host system will therefore ultimately occupy a significant proportion of the physical volumes, so that much of the space of the data storage media of the backing store is also wasted in storing the host-expired logical volumes.
In a complicated and lengthy process, the entire contents of an automated data storage library may be inventoried in order to identify the host-expired logical volumes. The library must be placed offline and made unavailable for use during the inventory process. Commonly assigned U.S. Pat. No. 5,870,732 describes a method for creating a new inventory of the physical volumes of data storage media and of the logical volumes stored on the physical media. A host system may be able to ascertain that many of the logical volumes have been expired by the host. However, in a multiple host system, one host conducting the inventory may be unable to identify the logical volumes expired by another host.
As the result, the actual removal of the expired logical volumes from the library server mapping database is not certain and, if done, will be as the result of a complicated and lengthy process.
An object of the present invention is to provide removal of host-expired logical volumes by the automated data storage library without requiring an inventory of the entire library.
Disclosed are a data storage library and library computer processor implemented methods for expiring logical volumes in response to expiration selection from a host. A library server maintains the mapping database which identifies each logical volume and maps the logical volumes to the data storage media. The library server additionally manages the logical volumes of the mapping database, the managing comprising expiring logical volumes from the mapping database, e.g., by reclaiming the data storage media, rewriting only the logical volumes which appear as active in the mapping database.
An input receives commands from a host system relating to the logical volumes, one of the commands comprising expiration selection of at least one of the logical volumes. A category of logical volumes will have been established at an operator station, the categories listed in a category table by a library manager together with at least one attribute of each category. The operator established category has a xe2x80x9cSCRATCHxe2x80x9d attribute, and additionally an expiration delay may be established for the category having the xe2x80x9cSCRATCHxe2x80x9d attribute.
The library manager responds to the received host expiration selection of any of the logical volumes, classifying the selected logical volume in the category having the xe2x80x9cSCRATCHxe2x80x9d attribute in the category table, identifying the selected logical volume, in a searchable database, as comprising the category having the xe2x80x9cSCRATCHxe2x80x9d attribute. Additionally, the library manager may calculate from the expiration delay an expiration time for the selected logical volume.
The library manager subsequently searches the searchable database for logical volumes identified as comprising the category having the xe2x80x9cSCRATCHxe2x80x9d attribute, and whose expiration time has passed. The library manager provides an indication to the library server that the searched identified logical volumes are expired, and the library server then expires the searched identified logical volumes from the mapping database.
The delay time serves as a recovery window, during which time the host may revive any logical volume that had been selected for expiration. The library manager reclassifies the logical volume into a category other than a category having the xe2x80x9cSCRATCHxe2x80x9d attribute.
For a fuller understanding of the present invention, reference should be made to the following detailed description taken in conjunction with the accompanying drawings.